1. Field of the Invention
This application is a National Stage Entry of International Application No. PCT/KR2016/011616 filed on Oct. 17, 2016, and claims the benefit of Korean Application No. 10-2016-0006986, filed on Jan. 20, 2016, all of which are hereby incorporated by reference in their entirety for all purposes as if fully set forth herein.
The present invention relates to carbon nanotube pellets, and more particularly, to a method of pelletizing carbon nanotubes to facilitate handling and processing of the carbon nanotubes.
2. Description of the Related Art
Carbon nanotubes exhibit insulating, conducting or semiconducting properties depending on their inherent chirality. Carbon nanotubes have a structure in which carbon atoms are strongly covalently bonded to each other. Due to this structure, carbon nanotubes have a tensile strength approximately 100 times greater than that of steel, are highly flexible and elastic, and are chemically stable. Carbon nanotubes are of industrial importance in the manufacture of composites because of their size and specific physical properties. Carbon nanotubes can find widespread applications in numerous fields, including electronic materials and energy materials. For example, carbon nanotubes are applicable to secondary batteries, fuel cells, electrodes of electrochemical storage devices (e.g., supercapacitors), electromagnetic wave shields, field emission displays, and gas sensors.
However, due to the low density of the bulk carbon nanotubes and scattering in the process due to the powder form of tens of micrometers of the carbon nanotubes, it may cause harm to the human body and malfunction of the electric appliance. In addition, there is a difficulty in dispersion due to a difference in apparent bulk density between pellets and powder-type polymers to be mixed.
For the above reasons, conventionally, the carbon nanotubes are usually provided by pelletization because of the increase in the density of the carbon nanotubes and the ease of handling and transportation thereof. In addition, the pelletized carbon nanotubes are convenient for use in various processing apparatuses. In the conventional method, in order to granulate or pelletize the carbon nanotubes, two different methods, that is, a method in which they are wet pelletized and then dried and a method in which they are dry pelletized are used.
Generally, dry pelletization uses a pelletizing drum comprising a horizontally disposed rotary tube, the interior of which is referred to as a pelletizing chamber. In order to granulate the carbon nanotube powder, it is produced by process in which the industrial powders are preliminarily densified and rolling from a rotating tube wall in a pelletizing drum to pelletize them. They are agglomerated by electrostatic forces and Van-Der-Waals forces that enable dry pelletization and are usually produced by applying a few tons of pressure during dry pellet formation. Therefore, there is a problem that the pellets can be destroyed again during the manufacturing process. The wet pelletization process is mainly performed by a liquid bridge and a capillary force between the carbon nanotubes. Conventionally, when mixing with carbon nanotubes by a wet pelletization method, excessive water is added because the distribution of water and binder is poor. In this case, the added water is usually removed by heat in a rotary drum dryer. Excessive water therefore increases the load on the dryer and, consequently, reduces the throughput of the product through the process. Excessive water also increases the energy and time required for drying. Therefore, uniform distribution of water and binder in the carbon nanotube mixture is very important in the pelletization process. Furthermore, if the components of the pellets are not mixed uniformly, the quality of the produced carbon nanotube pellets may not be constant.
To solve this problem, a method of treating a dispersant such as a surfactant in order to improve the dispersibility of pellets has been studied. However, there is still a problem that such a material may act as an impurity by remaining in the carbon nanotube pellets.